The present invention relates generally to motordriven electrical appliances such as electric shavers, and particularly to circuit means for use in such appliances which allow the appliances to automatically operate from electrical mains having a wide range of voltage levels.
With the present trend toward increased foreign travel the need has arisen for portable appliances operable from both the 110-120 volt mains or lines prevalent in the United States and North America, and from the higher 220-240 volt lines prevalent in Europe and much of the rest of the world. While this capability can invariably be obtained by the inclusion of multiple windings on the electric motor of the appliance, or by the inclusion of various types of resistance networks within the appliance, such circuits have heretofore been undesirably expensive and have necessitated that the user make a voltage selection prior to use of the appliance. Frequently, and particularly where the user is unfamiliar with the appliance or the voltage level of the lines in a foreign country, the appliance may be subjected to an over-voltage condition which may result in permanent damage to the appliance.
Accordingly, the need has arisen for a power supply circuit for use in electrical appliances which will automatically condition the appliances to operate from a variety of line voltages. Ideally, such a circuit would require no pre-selection of line voltage whatsoever by the user, would be economical to manufacture so as to not unduly cost-burden the appliance in the highly competitive appliance industry, and would not unduly add to the weight or detract from the reliability of the appliance. Furthermore, such a circuit would preferably provide minimal heat dissipation, allowing the shaver to run cool even after extended periods of use.
Therefore, it is a general object of the present invention to provide new and improved circuit means for an electrical appliance whereby the appliance may be operated over a wide range of line voltages.
It is another object of the present invention to provide new and improved circuit means for an electrical appliance which automatically condition the appliance to operate over a wide range of line voltages.
It is another object of the present invention to provide new and improved circuit means for an electrical appliance of the type having an electrical motor wherein the speed for the motor is maintained substantially constant over a wide range of line voltages.
It is another object of the present invention to provide economical circuit means for an electric shaver which allow the shaver to operate from a wide range of source voltages with minimum heat dissipation and with no manual pre-selection of source voltage.